I'd lean towards this explanation. The alternative would to have established a grand conspiracy between the Drews and a lot of other kids, which would have posed much more risk of exposing their Josh hoax before it could do the mischief they had in mind.
That would be one alternative, but neither of those is reasonable. Can you imagine the logistical nightmare of trying to run several fake accounts at once? And it seems unlikely that the Meiers would cover that up on behalf of their alleged tormenters. No, I think those were real accounts. It seems more likely that Josh was the only fake account, and the other kids were real kids telling their honest opinion about Megan’s behavior.